1. Field of the Invention
The invention pertains to a scale with a weighing cell, which is used during each weighing operation to generate weight signals representing the weight of a load, and with a signal processing system, which receives the weight signals for the purpose of generating:
weight data on the basis of the weight signals,
information determined on the basis of the weight data such as purchase prices, and/or
weighing data containing identification data which identify the weighing operation or group of associated weighing operations in question,
to an interconnected system with a scale of this type, and to methods for operating a scale of this type and the corresponding interconnected system.
2. Description of the Related Art
Scales of this type are used in, for example, retail shops and supermarkets for weighing individual products such as meat, sausage, cheese, fruit, and vegetables. In the usual case, the purchase prices for the weighed products are determined on the basis of the weight data and the base prices assigned to the merchandise. This base price can be entered directly on a keyboard or called up from a memory unit by the use of, for example, a code, which is read by a barcode reader. During the operation of conventional scales; several separate weighing operations are often carried out during the handling of an individual sales transaction, and the weighing data produced by such transactions must be processed all together and printed out, usually at the conclusion of the sales transaction. For this purpose, the weighing data are usually stored in bookkeeping memories assigned to the individual sales transactions. In the course of a sales transaction, it can also become necessary to use several scales and to continue to process the weighing data generated by the previously used scale together with those generated by the other scale. In known interconnected systems of scales, it is possible for this purpose to transmit these weighing data over appropriate data lines.
In view of the range of functions which the known scales must perform and especially in view of the operation of scales in an interconnected system, modern scales have a so-called PC architecture consisting of a conventional PC main board, a conventional graphics card, a display unit connected to the graphics card, a hard disk drive, possibly additional drives for reading other types of data storage media, and one or more interfaces, etc. The PC main board forms a part of the signal processing system. In addition, this signal processing system usually has a signal processing unit, which receives the weight signals transmitted from the weighing cell in the form of crude measurement data. In the signal processing system, the actual weight data representing the weight values are usually generated from the weight signals, which ate in the form of crude digital values, by the use of model-specific and machine-specific parameters; these weight data are then sent via an appropriate I/O port or an appropriate interface to the PC main board for further processing. This signal processing system of the known scales is usually separated physically from the PC main board and realized in the form of a separate circuit or card. This makes it very easy to ensure the calibration security required for the determination of the weight data representing the weight values.
In the known scales, the weight data determined by the signal processing system are read out from the signal processing system by a default program and subjected to further processing to determine, for example the price data. In addition, this default program can also be used to transmit the weight data and other information derived from the weight data, for example, to other machines, especially to other scales. With respect to the relevant calibration laws, the programs used for the processing and/or transmission of weighing data and the associated hardware must be officially inspected and approved by the authorized standards institution. This inspection must usually be repeated every time a new function is added to the program or every time a user wants to use one of his own program such as an inventory management program, a bookkeeping program, or a merchandise management application, on the scale in addition to the already inspected default program. For this reason, the known PC scales are often not used to run programs of this type and thus often not used as components of a higher-level merchandise management system, because such programs or systems are frequently modified and it is not economically feasible to have the entire system inspected again according to the calibration regulations every time one of these modifications is made.
This problem was addressed as early as 1995, in which year the xe2x80x9cWELMEC Guide to the Testing of Software for Non-Automatic Scalesxe2x80x9d was published. This guide compiles the key requirements for protecting software subject to the calibration law against unintentional and intentional changes as well as the key requirements on the software for freely programmable modules or for accessory units of scales subject to the calibration law. In agreement with its stated goals, however, this guide describes only the most essential properties of the scales and of the software used to operate the scales; it does not provide any concrete technical solutions. Only with respect to the protection of the software subject to the calibration law, which comprises both the functions subject to the calibration law such as:
the weight determination,
the price calculation,
the visual display of these data, and
the printout of these data,
and the model-specific and machine-specific parameters subject to the calibration law, it is proposed, as a way of providing security against intentional and unintentional changes, that a check sum be calculated via the machine code which contains the program segments and parameters subject to the calibration law and that the program of the software subject to the calibration law be prevented from starting if is determined on the basis of a comparison of this check sum with a predetermined checksum that a change has occurred in the machine code.
With respect to the communications between the software subject to the calibration law and the freely programmable software segments not subject to the calibration law, the use of a non-reactive software interface is proposed, a software interface being defined as xe2x80x9cnon-reactivexe2x80x9d when only a precisely defined number of parameters and functions of the software segment subject to the calibration law can be affected via this interface and the two software segments cannot exchange any data over any other (undefined) link.
These solutions make it possible to operate freely programmable program segments on scales subject to the calibration law without the necessity of having an official inspection and approval procedure performed in accordance with the calibration law every time a modification is made to the program segments subject to the calibration law. Nevertheless, the approaches suggested in the WELMEC Guide still do not make it possible to read out data such as weight data and data derived from them, especially price data, which have been acquired with the help of functions subject to the calibration law, from the protected program segment of a scale, to process them with a program segment not subject to the calibration law, or to transmit them to a different scale and to read them back again to the program segment subject to the calibration law of this or a different scale, because the measures indicated above cannot prevent the manipulation of the weighing data by the freely programmable program segment or the visual display or printout of these manipulated weighing data on a device subject to the calibration law such as a scale.
In view of these problems of the state of the art, the invention is based on the task of providing a scale of the type described above which, while ensuring calibration security, makes it possible to transmit data subject to the calibration law between individual program segments or units by the use of freely programmable programs not subject to the calibration law.
This task is accomplished according to the invention by an elaboration of the known scales, which is characterized essentially in that the signal processing system has an encryption unit, by means of which, on the basis of at least some of the weighing data, encryption data can be generated, and in that the signal processing system can be used to output a data record containing at least the portion of the weighing data used to generate the encryption data together with the encryption data.